javascript

Chapter 5: Reference Types
To create a date object, use the new operator along with the Date constructor, like this:
var now = new Date();
When the Date constructor is used without any arguments, the created object is assigned the current
date and time. To create a date based on another date or time, you must pass in the millisecond
representation of the date (the number of milliseconds after midnight, January 1, 1970 UTC). To aid in
this process, ECMAScript provides two methods: Date.parse() and Date.UTC() .
The Date.parse() method accepts a string argument representing a date. It attempts to convert the
string into a millisecond representation of a date. ECMA - 262 doesn ’ t define which date formats Date
.parse() should support, so its behavior is implementation - specific and often locale - specific. Browsers
in the United States typically accept the following date formats:
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month/date/year (such as 6/13/2004)
month_name date, year (such as January 12, 2004)
day_of_week month_name date year hours:minutes:seconds time_zone (such as Tue May 25
2004 00:00:00 GMT - 0700)
For instance, to create a date object for May 25, 2004, the following code can be used:
var someDate = new Date(Date.parse(“May 25, 2004”));
If the string passed into Date.parse() doesn ’ t represent a date, then it returns NaN . The Date
constructor will call Date.parse() behind the scenes if a string is passed in directly, meaning that the
following code is identical to the previous example:
var someDate = new Date(“May 25, 2004”);
This code produces the same result as the previous example.
There are a lot of quirks surrounding the Date type and its implementation in
various browsers. There is a tendency to replace out - of - range values with the
current value to produce an output, so when trying to parse “ January 32,
2007 ” , some browsers will interpret it as “ February 1, 2007 ” , whereas Opera
tends to insert the current day of the current month, returning “ January
current_day, 2007 ” . This means running the code on September 21 returns
“ January 21, 2007 ” .
The Date.UTC() method also returns the millisecond representation of a date, but constructs that value
using different information than Date.parse() . The arguments for Date.UTC() are the year, the zero -
based month (January is 0, February is 1, and so on), the day of the month (1 through 31), and the hours
(0 through 23), minutes, seconds, and milliseconds of the time. Of these arguments, only the first two
(year and month) are required. If the day of the month isn ’ t supplied, it ’ s assumed to be 1, while all other
omitted arguments are assumed to be 0. Here are two examples of Date.UTC() in action:
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